1. Field of the Invention
The present invention relates to an apparatus, method, computer program for processing an image, and a recording medium storing the computer program. More particularly, the present invention relates to an enhancement process of a high-frequency component of input video data with noise caused image degradation reduced by performing image correction with the input video data enhanced and by increasing the degree of enhancement of the input video data as the intensity of the high-frequency component of the input video data increases.
2. Description of the Related Art
Known video apparatuses processing a variety of video data such as a video signal improve image quality by enhancing a high-frequency component of the data.
Japanese Unexamined Patent Application Publication No. 2001-298621 discloses a technique that extracts a high-frequency component using a non-linear smoothing filter and improves contrast and sharpness of image. As shown in FIG. 15, an image processing circuit 1 disclosed in Japanese Unexamined Patent Application Publication No. 2001-298621 limits a bandwidth of an input video signal S1 using a non-linear smoothing filter 2 such as a two-dimensional ε filter, and smoothes the input video signal S1 with an edge component thereof preserved, thereby outputting a video signal S2. The image processing circuit 1 subtracts the video signal S2 output from the non-linear smoothing filter 2 from the input video signal S1 using a subtractor circuit 3, thereby outputting a signal S4. The signal S4 has a high-frequency component of the video signal S1 with the edge component reduced therefrom. The image processing circuit 1 multiplies the high-frequency component signal S4, thereby adjusting the resulting product in level using a multiplier circuit 4. An adder circuit 5 in the image processing circuit 1 adds the output of the multiplier circuit 4 to the output signal S2 of the non-linear smoothing filter 2. The image processing circuit 1 thus outputs a video signal S5 with the edge component not enhanced but with contrast and sharpness of image improved.
In accordance with the known high-frequency region enhancement method, a noise component is also enhanced and image degradation results. Such a noise component becomes pronounced in an image of the sky, for example, where a high-frequency component is low in level and has no significant meaning in the image.